The present invention relates generally to semiconductor devices and their fabrication and, more particularly, to semiconductor devices and their manufacture involving dielectrics used with transistors.
The electronics industry continues to rely upon advances in semiconductor technology to realize higher-functioning devices in more compact areas. For many applications, realizing higher-functioning devices requires integrating a large number of electronic devices into a single silicon wafer. In addition, many of the individual devices within the wafer are being manufactured with smaller physical dimensions. As The number of electronic devices per given area of the silicon wafer increases, and as the size of the individual devices decreases, the manufacturing process becomes difficult.
A large variety of semiconductor devices have been manufactured having various applications in numerous disciplines. Such silicon-based semiconductor devices often include metal-oxide-semiconductor (MOS) transistors, such as p-channel MOS (PMOS), n-channel MOS (NMOS), complementary MOS (CMOS), bipolar complementary MOS (BiCMOS), and bipolar transistors.
Each of these semiconductor devices generally includes a semiconductor substrate on which a number of active devices are formed. The particular structure of a given active device can vary between device types. For example, in MOS transistors, an active device generally includes source and drain regions and a gate electrode which modulates current between the source and drain regions.
As devices are scaled below 0.18 microns, gate insulator thicknesses reach the quantum mechanical regime. One gate insulator material used in this regime is silicon dioxide. Current research indicates that silicon dioxide thicknesses of 20-25 angstroms will result in unacceptably large tunneling currents. To alleviate this problem, research has begun on alternatives to silicon dioxide that have larger dielectric constants. This allows the use of thicker gate insulators, diminishing the gate tunneling current without reducing the gate capacitance. However, large capacitance is not desirable in the source-drain overlap regions of the gate because it increases the gate to source-drain, or overlap, capacitance and degrades transistor performance. The gate-to-drain capacitance is particularly critical for transistor performance as it is amplified during switching due to the Miller effect.
Previous work on this problem has mostly focused on thickening the gate oxide over the source-drain region to reduce overlap capacitance. This provides only a modest reduction in overlap capacitance and creates stress in the gate.
With the demands for increasing the density of such MOS-based circuits continuing to escalate, there is an ongoing need to reduce the amount of real estate consumed by various aspects of the circuits and to minimize the complexities and deficiencies resulting from manufacturing processes.
The present invention is directed to a transistor gate insulator material that not only meets the compact size requirements of higher-functioning devices but also adequately insulates the gate and channel regions and improves the transistor performance. The present invention is exemplified in a number of implementations and applications, some of which are summarized below.
According to an example embodiment, the present invention is directed to a semiconductor device that includes a transistor comprising source and drain regions separated by a channel region. A gate is formed over the channel region, over part of the source region, and over part of the drain region. An insulator region is configured and arranged to insulate the gate from the channel region and from the source and drain regions. The insulator region has a first material arranged substantially over the channel region and providing a high dielectric constant, and a second material arranged substantially over part of the source region and over part of the drain region and providing a significantly lower dielectric constant.
In another example embodiment, the present invention is directed to a method for manufacturing a semiconductor device. The device includes source and drain regions separated by a channel region, and an insulator region. The insulator region is over-etched to form recesses at corners of the gate adjacent the source and drain regions. A second material is formed in the recesses.
In yet another example embodiment, a semiconductor device that includes a transistor having source and drain regions separated by a channel region is provided. A gate is formed over the channel region, over part of the source region, and over part of the drain region. An insulator region is configured and arranged to insulate the gate from the channel region and from the source and drain regions. The insulator region has means, arranged over the channel region, for providing a high dielectric constant. The insulator region also has means, arranged over the part of the source region and over the part of the drain region, for providing a significantly lower dielectric constant.